Usually, a music box, or an orgel is referred to an automatically played music instrument toy and is applied to clock, finger ring, neck lace, toy and so on. There are two types of music box, the first type music box comprises a disc having a plurality of protrusions cut and bent with predetermined pattern on one side and a metal bar traversing the surface of the disc and having a plurality of pins extending downward against the disc. When the disc turns, the protrusions of the disc hit the pins of the metal bar to generate the sound.
The second type music box comprises, as the basic parts, a rotating cylindrical drum 1 and a metal vibration plate 3 disposed at the side of the cylindrical drum 1 as shown in FIG. 1. The cylindrical drum 1 has a plurality of protrusions 2 with the predetermined pattern on the circumferential surface of it, and the vibration plate 3 has a plurality of sound generation pins 5 with the different lengths corresponding to the different sounds of scale. When the protrusions 2 hit the sound generation pins 5 of the vibration plate 3, the sound generation pins 5 may vibrate and generate the corresponding sounds.
To make the vibration plate 3 having the sound generation pins 5, the metal plate should go through the slit-cutting process to form the sound generation pins 5 with different length. To do this, the metal plate should be machined for the sound generation pins 5 to be formed on the base 4 of the vibration plate 3 in parallel. And the metal plate should be machined for the thickness of the sound generation pins 5 to be thinner than that of the base 4, and the lengths of the sound generation pins 5 to be different from each other corresponding to the sound scale.
The sound generation pin 5 has a natural frequency according to the length of it, and a little difference of the length may result in the difference of the sound. In general, in consideration of the convenience of machining and productivity, the front end of the base 4 of the vibration plate 3 is machined to form an inclined line. But, this process of machining could not achieve precise dimension of the sound generation pins 5 because the lengths of them are machined in one time. So the vibration plate 3 of the conventional music box could not achieve precise sound scale.